This invention relates to laser welding and, more particularly, to methods of joining multiple workpieces using a laser and added powdered metal to create a low porosity weld and/or fill in gaps between workpieces.
Laser welding when used to join metal workpieces, forms a xe2x80x9ckeyholexe2x80x9d of vaporized metal through which the laser beam heats and melts portions of a first and adjacent workpieces. If the workpieces contain metals having different melting points, either as coating or as an alloy, vaporization of the low melting temperature metal or coating will occur while the steel, or other metal substrate is melting. The vapor created may then become trapped as the molten metal is cooled creating porosity and voids in the weld between the workpieces. In addition, if a gap exists between the workpieces, the volume of the molten weld pool may not be adequate to bridge the gap between the workpieces, resulting in a discrepant weld.
The present invention provides an improved method of laser welding using an injector to dispense powdered metal into the molten weld pool. The method is useful for welding coated metals, such as galvanized steel, and for welding workpieces having gaps between the workpieces along the weld seam. During welding, the laser locally heats up the workpieces, forming a keyhole creating molten metal through the first workpiece and into the adjacent workpieces.
In the case of galvanized steel or other metals containing a lower melting temperature metal, the zinc or other metal may vaporize while the steel or other metal substrate is being melted by the laser. The vapor may then be trapped in the weld, resulting in a low quality porous weld.
To avoid this, powdered metal is injected into the molten weld pool. A powdered metal is selected which has an affinity for the lower melting temperature metal. As the powdered metal is injected into the molten weld pool, heat from the molten metal and the laser beam melt the powder. As the powder melts, it forms a chemical or metallurgical bond with the lower melting temperature metal, creating an alloy having a higher vaporization temperature. Increasing the vaporization temperature reduces vapor formation, thereby avoiding weld porosity and spatter.
In the case of workpieces having excessive gaps between them, the workpiece metal melted by the laser may be inadequate to bridge the gaps and form a weld connecting the workpieces. To avoid this, powdered metal is injected into the molten weld pool. The powdered metal may be similar to the metal of the workpieces or, if either of the pieces is coated, may be selected to react with the coating as well. In either case, the powdered metal increases the volume of the molten metal, which can be used to bridge the gaps between the workpieces. Finally, the molten metal is cooled to form a weld, free of porosity and filling any gaps between the workpieces.